The Delta Green wiki

Dholes are huge, worm-like entities that can be miles long. They burrow under the planet's crust, where they grow and multiply. Some authors compare them to a 'planet virus'. They nest inside a planet, then breed and overbreed, until the planet is a wrecked shell, like what the Ebola virus does to a cell. The end result of a dhole infection is the destruction of the planet. There have been no confirmed reports of dholes on Earth.

Some have suggested that the dholes are the source of myths about the Midgard Serpent, a worm large enough to encircle the world. It might also be related to the Biblical Leviathan. That would imply that dholes could live on a planet for centuries before destroying it.

The one place that humans have encountered dholes is in the Dreamlands. Like a handful of other creatures, dholes have been reported on both sides of the Wall of Sleep. This makes many wonder if there is more to these creatures than meets the eye.

It has been theorized that dholes are connected in some way with Cthonians, another subterranean race, either as relatives or enemies. There has been one reference to a Shai Hulud, a sort of god-king of the dholes, but it held nothing in the way of detail.

Another author speculated that dholes may be the ur-form of Yig, the father of serpents. The anthropoid image usually associated with Yig may just be a human error. The same author suggests that Yig may be be connected to the Lloigor, another serpent-like race.